Submerged membranes have been applied with variable success. One of the key problems is membrane fouling and membrane maintenance. Numerous inventions have used air to reduce the membrane fouling. In addition there are the traditional methods of solid separation in a liquid. Such traditional methods use clarifiers with and without settling tubes or inclined settling plates, or air flotation systems, where high pressure dissolved air, or induced air or froth flotation systems are used to separate the solids and float the solids to the surface and then remove the solid sludge/skim layer with a skimmer or skim/float separation system.
U.S. Pat. No. 7,160,454 B2 is an invention that uses air and small pore, small diameter submerged membranes. Patent Application US 2007/0205146 A1 has provided an application on the design and assembly of a submerged membrane for use with invention U.S. Pat. No. 7,160,454 B2.
Patent Application US 2004/0217058 A1 uses the combination of dissolved air flotation and submerged membranes where different zones make up the operation of the invention application.
U.S. Pat. No. 6,344,147 B1 is an invention using perforated membranes in the bottom of a flotation tank to create small air bubbles to float solids to the surface in a flotation water or wastewater treatment system.
Journal papers authored by Lazaridis et al (Aristotle University, Greece) in July 2003 and July 2004, discuss the benefits of froth flotation with submerged membranes but do not discuss the effects of the use of coarse membranes and the spacing and precoating of membranes in connection with froth flotation.
Journal papers authored by Benjamin et al (Washington State University) in 2008 talk about the benefit of precoats on membranes for organic removal and membrane maintenance.